This invention relates to blow molded articles and more particularly to a method for applying prefabricated parts to articles blow molded from a thermoplastic material.
Considerable difficulty has been encountered in the past in applying labels to bottles and other containers blown from polyvinyl chloride (PVC), polyethylene and other thermoplastic materials. Early attempts generally consisted either of gluing a preprinted paper label to the finished bottle or directly printing the label on the bottle. However, problems occurred due to the complex curved surfaces of the blow bottle. Other attempts were made at printing directly on the interior surface of a mold in which the bottle was blown. During the blowing process, the printing is transferred to the bottle when the hot plastic is blown into contact with the mold surfaces.
In a modification of this system, the printing or bottle decoration is placed on a leaf or foil having a layer of either thermoplastic or gluable material. The leaf is then positioned within the mold cavity prior to blowing the bottle. When the bottle is blown, the thermoplastic bottle material is forced into contact with and adheres to the leaf to form a complete decorated bottle within the mold cavity. A system of this type is shown, for example, in U.S. Pat. No. 3,267,186 which issued Aug. 16, 1966. In the method disclosed in this patent, the label is cut from a strip of preprinted labels by means of a stamp and is held against the face of the stamp by vacuum passages within the stamp. The stamp and label are then inserted into a opening in the mold cavity to a position wherein the face of the stamp forms a surface portion of the mold cavity. When a bottle is then blown within the mold cavity, the preprinted label adheres to the bottle. Apparatus for manufacturing bottles in accordance with this method is quite expensive due to the high cost for the bottle blowing mold which must provide an opening for receiving the stamp and must be mounted to cooperate with the stamp for positioning the labels or leafs within the mold cavity. Furthermore, it is only practical to place a single label on a portion of the bottle with apparatus of this type while other prior art techniques such as labeling the bottle after blowing permits the placement of multiple labels on the bottle at different locations. Another disadvantage with prior art techniques of applying labels to bottles during the final blow molding is in obtaining a good bond between such labels and the bottle. When the label is first positioned within the mold prior to blowing the bottle, the cooler mold surfaces cool the label sufficiently to prevent a welding or fusion between the label and the thermoplastic bottle material when a parison is blown into contact with the mold surfaces and the label. As a consequence, the label may subsequently separate from the bottle.